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    Subject[PATCH 3.16 191/357] ARM: 8178/1: fix set_tls for !CONFIG_KUSER_HELPERS
    Date
    3.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Nathan Lynch <nathan_lynch@mentor.com>

    commit 9cc6d9e5daaa147a9a3e31557efcb331989e77be upstream.

    Joachim Eastwood reports that commit fbfb872f5f41 "ARM: 8148/1: flush
    TLS and thumbee register state during exec" causes a boot-time crash
    on a Cortex-M4 nommu system:

    Freeing unused kernel memory: 68K (281e5000 - 281f6000)
    Unhandled exception: IPSR = 00000005 LR = fffffff1
    CPU: 0 PID: 1 Comm: swapper Not tainted 3.17.0-rc6-00313-gd2205fa30aa7 #191
    task: 29834000 ti: 29832000 task.ti: 29832000
    PC is at flush_thread+0x2e/0x40
    LR is at flush_thread+0x21/0x40
    pc : [<2800954a>] lr : [<2800953d>] psr: 4100000b
    sp : 29833d60 ip : 00000000 fp : 00000001
    r10: 00003cf8 r9 : 29b1f000 r8 : 00000000
    r7 : 29b0bc00 r6 : 29834000 r5 : 29832000 r4 : 29832000
    r3 : ffff0ff0 r2 : 29832000 r1 : 00000000 r0 : 282121f0
    xPSR: 4100000b
    CPU: 0 PID: 1 Comm: swapper Not tainted 3.17.0-rc6-00313-gd2205fa30aa7 #191
    [<2800afa5>] (unwind_backtrace) from [<2800a327>] (show_stack+0xb/0xc)
    [<2800a327>] (show_stack) from [<2800a963>] (__invalid_entry+0x4b/0x4c)

    The problem is that set_tls is attempting to clear the TLS location in
    the kernel-user helper page, which isn't set up on V7M.

    Fix this by guarding the write to the kuser helper page with
    a CONFIG_KUSER_HELPERS ifdef.

    Fixes: fbfb872f5f41 ARM: 8148/1: flush TLS and thumbee register state during exec

    Reported-by: Joachim Eastwood <manabian@gmail.com>
    Tested-by: Joachim Eastwood <manabian@gmail.com>
    Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
    Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/include/asm/tls.h | 2 ++
    1 file changed, 2 insertions(+)

    --- a/arch/arm/include/asm/tls.h
    +++ b/arch/arm/include/asm/tls.h
    @@ -81,6 +81,7 @@ static inline void set_tls(unsigned long
    asm("mcr p15, 0, %0, c13, c0, 3"
    : : "r" (val));
    } else {
    +#ifdef CONFIG_KUSER_HELPERS
    /*
    * User space must never try to access this
    * directly. Expect your app to break
    @@ -89,6 +90,7 @@ static inline void set_tls(unsigned long
    * entry-armv.S for details)
    */
    *((unsigned int *)0xffff0ff0) = val;
    +#endif
    }

    }



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